1. Field of the Invention
The present invention relates to a wheel support bearing assembly for rotatably supporting a vehicle wheel or the like.
2. Description of the Prior Art
As a wheel support bearing assembly for supporting a vehicle drive wheel, such a wheel support bearing assembly as shown in FIG. 3 of the accompanying drawings has hitherto been suggested (See, for example, the Japanese Laid-open Patent Publication No. H9-164803). Referring to FIG. 3, the wheel support bearing assembly shown therein is of a type, in which double row balls 25 as rolling elements are interposed between raceway surfaces 23 and 24, opposed to each other, defined respectively in an outer member 21 and an inner member 22. The inner member 22 is made up of a hub unit 28, having a wheel mounting hub flange 29a defined in an outer periphery thereof, and an inner ring 30 mounted on an outer periphery of an inboard end of the hub unit 29. The hub unit 29 has a center bore 31 defined in a center portion thereof, into which a stem portion 33a of an outer ring 33 of a constant velocity universal joint, and a stepped face 33b of the constant velocity universal joint outer ring 33 is urged against an inboard end face 30a of the inner ring 30. In this condition, with a nut 34 threadingly mounted on a free end of the stem portion 33a, the inner member 22 is constrained axially in position by and between the constant velocity universal joint outer ring 33 and the nut 34.
In this suggested example, the inner ring 30 is externally mounted on an inner ring mounting area 35, which is defined in the outer periphery of the inboard end of the hub unit 28 and is so configured as to represent an annular recess, a step 36 is formed in an inner periphery of an inboard end of the inner ring 30, and the inboard end of the hub unit 29 is radially outwardly deformed by diameter expansion to crimp the step 36 in the inner ring 30. In this way, an undesirable separation of the inner ring 30, which would occur by the effect of an external force during assemblage onto an automotive vehicle body, is avoided.
It is, however, been found that the wheel support bearing assembly of the type discussed above has the following problems:
(1) Since a crimped portion 29b of the hub unit 29 is large in size, as shown in FIG. 4 showing a portion of FIG. 3 on an enlarged scale, the radial setback of the step 36 formed in the inboard end portion of the inner ring 30 must be about 5 to 7 mm in terms of the difference in radius between the inner ring mounting area 35 and the step 36. If the setback of the step 36 is increased, the surface area of the inboard end face 30a of the inner ring 30 will decrease and as a result, the surface pressure of contact with the stepped face 33b of the constant velocity universal joint outer ring 33 will hence increase. For this reason, it will constitute a cause of generation of frictional wear and abnormal noise.
(2) If an attempt is made to allow the crimped portion 29b of the hub unit 29 to be accommodated inwardly (outboardly) of the inboard end of the inner ring 30, it is necessary that the axial length of the step 36 in the inner ring 30 as shown in FIG. 4 must be 7 to 8 mm. Such an increase of the axial length of the step 36 results in a tendency of the inner ring step 36 to be positioned on an extended line L of the ball contact angle θ and there is the possibility of considerable deformation of the inner ring by the effect of a load bearing during the operation, resulting in reduction in lifetime. Also, such an increase of the axial length of the inner ring step 36 results in decrease of the mounting length (surface area), over which the inner ring 30 is mounted on the hub unit 29, and, therefore, an inner ring creepage may occur, resulting in the possibility of the bearing lifetime being reduced. Those problems may be alleviated if the widthwise dimension (the axial length) of the inner ring 30 as a whole is increased, but increase of the widthwise dimension would require an extra space the widthwise direction.
(3) In addition, since the crimped portion 29b of the hub unit 29 is large in size, a crimping punch will interfere with the inner ring 30 during the orbital forging process, resulting in difficulty to achieve the forging.